Those terms are a bit overloaded. There isn’t really any way to compare them as they are orthogonal concepts / tools.
Take a look at the image here:
https://www.pulumi.com/docs/pulumi-cloud/deployments/
“Cloud Platform Automation” is the entire thing. The right most arrow shows which part is the “Pulumi Deployments Platform”. “Remote Automation API” is a way to trigger a deployment programatically.